The matrix element for a radiative transition of an excited baryon to its ground state \(\mathcal {M}(R\rightarrow N\gamma ^*\) ) can be expressed as coherent sum of helicity amplitudes \(A_{3/2}(q^2)\) , \(A_{1/2}(q^2)\)  and \(S_{1/2}(q^2)\) , defined in the resonance decay frame [1]}, [2]}.
The amplitudes describe transitions for a resonance of given spin \(J\)  and helicity \(\lambda ^*\)  to a nucleon with the helicity \(\lambda =\pm 1/2\)  and a photon with \(\lambda _\gamma =1,0\) .
The projection axis is defined to be along the photon momentum and hence \(\lambda ^*=-\lambda +\lambda _\gamma >\)  (please note that one can consider only \(\lambda _\gamma \ge 0\)  due to conserved parity).
The first two amplitudes are related to the transverse photon polarization (\(\lambda _{\gamma }= 1\) ) while the last one is related to the longitudinal photon polarization (\(\lambda _\gamma =0\) ).
Transverse helicity amplitudes have been determined in the space-like region for several resonances in electro- and photo-production experiments.
However, they are unknown in the time-like region which is only accessible by their Dalitz decays \(R\rightarrow N\gamma ^*\)  (for a review see [2]}).
The respective differential decay width \(d\Gamma (R\rightarrow Ne^+e^-)/dM_{\ell ^+\ell ^-}\)  can be expressed similar to Eq. REF  but here with the \(d\Gamma (R\rightarrow N\gamma ^*)\)  given as a function of three covariant or Magnetic (\(G_M(q^2)\) ), Electric (\(G_E(q^2)\) ) and Coulomb (\(G_C(q^2)\) ) eTFF's.
The form factors are related to the helicity amplitudes discussed earlier (respective relations can be found in [1]}).
The relations for the \(\Delta (1232)\)  resonance were introduced by Jones and Scadron [5]} and for higher mass resonances by Devenish, Eisenschitz and Körner [6]}.
It should be noted that the Coulomb form factor couples only to the \(S_{1/2}\)  while the electric and the magnetic form factors couple to all three helicity amplitudes.
